1. Field of the Invention
A plastic pulley for driving drum for washing machine into rotation.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The present patent application for industrial invention relates to a plastic pulley for driving drum 1 for washing machine into rotation.
FIGS. 1 and 1A respectively show a drum, pulley and motor assembly and a tub of washing machine according to the prior art. The washing machine comprises a drum (100) to contain laundry. The drum (100) is revolvingly mounted inside a tub (101).
A shaft (102) fixed to the drum protrudes axially on the back of the drum. The shaft (102) of the drum is revolvingly mounted inside a bearing assembly (103) fixed to the hack wall of the tub (101).
A pulley (P) is splined on the shaft (102) of the drum. An electric motor (105) fixed to the tub (101) is used to drive the pulley (P) and the drum (100) into rotation. The electric motor (105) is provided with a drive shaft with pinion (107) that drives into rotation a belt (108) wound on the periphery of the pulley (P).
So the pulley (P) transfers the rotational torque of the motor (105) to the shaft (102) of the drum in order to rotate the drum (100) during washing cycles. It must be considered that current models of washing machines can be loaded with several kilograms of laundry, and therefore the drum (100) is subject to high weight, especially when laundry is soaked in washing water. Moreover, the rotational speed of the drum must be very high, since washing machines with spinning cycles higher than 1400 rpm are often required. Also, laundry takes irregular positions during the rotation of the drum (100), thus forcing inclination of shaft (102).
Evidently, the pulley (P) of the shaft of the drum is subject to high stress during operation of washing machine. Tension of belt (108), accelerations of motor (105), fixing system to shaft (102) and high temperature contribute to stress the pulley (P).
For this reason, pulleys of the shaft of the drum are generally made of high-resistance metal material. Nevertheless, such metal pulleys are impaired by some inconveniences caused by high costs.
In order to remedy said inconvenience at least partially, plastic pulleys have been devised, such as the one illustrated in patent application PCT WO2007/057234. Said plastic pulley is provided with traditional configuration, comprising a hub, a peripheral crown and a plurality of radially extending spokes that connect hub to peripheral crown. Evidently, such a pulley is not able to meet resistance requirements, unless it is made with high thickness. This would obviously result in increased volume and costs.
Patent application EP 2 159 314 discloses a plastic pulley for washing machine, provided with radial spokes originating from hub and branching of into a fork connected to external rim. In order to guarantee resistance of pulley, also according to this inventive solution, arms and forks have high width, with consequent material waste. Moreover, such a pulley is impaired by lack of stability, being subject to high torsional moment. These problems are solved by further increasing thickness and width of said arms and forks.